Interdecadal Change of the Northward Jump Time of the Western Pacific Subtropical High in Association with the Pacific Decadal Oscillation

In this paper, the northward jump time of the western Pacific subtropical high (WPSH) is defined and analyzed on the interdecadal timescale. The results show that under global warming, significant interdecadal changes have occurred in the time of the WPSH northward jumps. From 1951 to 2012, the time of the first northward jump of WPSH has changed from continuously early to continuously late, with the transition occurring in 1980. The time of the second northward jump of WPSH shows a similar change, with the transition occurring in 1978. In this study, we offer a new perspective by using the time of the northward jump of WPSH to explain the eastern China summer rainfall pattern change from north-abundant-south-below-average to south-abundant-north-below-average at the end of the 1970s. The interdecadal change in the time of the northward jump of WPSH corresponds not only with the summer rainfall pattern, but also with the Pacific decadal oscillation (PDO). The WPSH northward jump time corresponding to the cold (warm) phase of the PDO is early (late). Although the PDO and the El Nio-Southern Oscillation (ENSO) both greatly influence the time of the two northward jumps of WPSH, the PDO's effect is noticed before the ENSO's by approximately 1-2 months. After excluding the ENSO influence, we derive composite vertical atmospheric circulation for different phases of the PDO. The results show that during the cold (warm) phase of the PDO, the atmospheric circulations at 200, 500, and 850 hPa all contribute to an earlier (later) northward jump of the WPSH.